I had a complete hysterectomy when I was 28 and immediately began HRT. I'm now 59 and still using HRT. My mother is 82 and is still using HRT. I think how long you take the meds is between you and your doctor and the risk factors you may or may not have.
Some women do very well without HRT and some do not. Your around the age where natural menopause would be happening, but you've had a complete hysterectomy so you are not and will not be getting natural hormones in to your system. You can always try to stop the meds and see how you do. I know I'm not answering your question but it's really hard to say how long you will need to be on them. You may be able to stop with no problems like hot flashes, or you may have to be on them much longer.